The past decade has seen intense interest in the characterization, synthesis and medicinal development of polyketide/macrolide natural products such as the bryostatins, discodermolides, spongistatins, epothilones, etc. as extraordinarily potent anti-cancer agents. In many cases, only exceedingly limited quantities of these (often marine) natural products are available from natural sources/fermentation, and this has greatly hampered efforts to more fully evaluate their biological/medicinal profile. The recent synthesis of ~60 g of discodermolide by a large group of Novartis chemists with enormous effort, time, and expense both underscores the need for large amounts of these compounds and provides a useful benchmark as to the state of the art in terms of synthetic accessibility. It is imperative, therefore, that synthetic organic chemists continue to provide significantly simpler methods for the synthesis of such compounds. Success toward this ambitious goal would impact not just the supply of these compounds, but efforts to develop analogs with improved pharmacological profiles as well. The present proposal details the development of reactions that will establish high levels of structural and stereochemical complexity in operationally trivial, environmentally sound, and scalable processes. This will be achieved through the orchestration of tandem reactions that assemble simple, principally hydrocarbon fragments into large segments of the target natural products that contain as many as three stereocenters. Importantly, the conceptual foundation for these methods involves the use of Lewis acidic silanes, compounds that are extraordinarily straightforward and inexpensive to synthesize on large scales. Following the development of these methodologies, we will demonstrate their effectiveness by accomplishing brief and efficient syntheses of important natural products such as zincophorin, dictyostatin, and the C(1)-C(28) ABCD fragment and the C(29)-C(51) EF fragment of the spongistatins. The targets have been selected for their biological importance and because it is our goal to improve the step economy with which such structures may be prepared.
Polyketide natural products are a rich source of biologically active compounds with extraordinary medicinal potential as antibiotics and as anti-cancer agents. However, very often they are available from natural sources in only minute quantities, insuffcient for their full biological profile to be investigated. This proposal seeks to develop efficient methods for the synthesis of gram-scale quantities of such compounds to aid in their biological evaluation and development.
|Foley, Corinne N; Leighton, James L (2015) A Highly Stereoselective, Efficient, and Scalable Synthesis of the C(1)-C(9) Fragment of the Epothilones. Org Lett 17:5858-61|
|Ho, Stephen; Sackett, Dan L; Leighton, James L (2015) A "methyl extension" strategy for polyketide natural product linker site validation and its application to dictyostatin. J Am Chem Soc 137:14047-50|
|Foley, Corinne N; Leighton, James L (2014) Beyond the Roche ester: a new approach to polypropionate stereotriad synthesis. Org Lett 16:1180-3|
|Tanis, Paul S; Infantine, Joshua R; Leighton, James L (2013) Exploiting pseudo C2-symmetry for an efficient synthesis of the F-ring of the spongistatins. Org Lett 15:5464-7|
|Suen, Linda M; Steigerwald, Michael L; Leighton, James L (2013) A new and more powerfully activating diamine for practical and scalable enantioselective aldehyde crotylsilylation reactions. Chem Sci 4:2413-2417|
|Ho, Stephen; Bucher, Cyril; Leighton, James L (2013) A highly step-economical synthesis of dictyostatin. Angew Chem Int Ed Engl 52:6757-61|
|Reznik, Samuel K; Leighton, James L (2013) Toward a more step-economical and scalable synthesis of spongistatin 1 to facilitate cancer drug development efforts. Chem Sci 4:1497-1501|
|Harrison, Tyler J; Rabbat, Philippe M A; Leighton, James L (2012) An "aprotic" Tamao oxidation/syn-selective tautomerization reaction for the efficient synthesis of the C1-C9 fragment of fludelone. Org Lett 14:4890-3|
|Chalifoux, Wesley A; Reznik, Samuel K; Leighton, James L (2012) Direct and highly regioselective and enantioselective allylation of Î²-diketones. Nature 487:86-9|
|Reznik, Samuel K; Marcus, Brian S; Leighton, James L (2012) Complex fragment coupling by crotylation: A powerful tool for polyketide natural product synthesis. Chem Sci 3:3326-3330|
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